Herbicidal 2-sulfinyl and 2-sulfonyl pyridine N-oxide derivatives

ABSTRACT

Certain 2-sulfinyl and 2-sulfonyl pyridine N-oxide derivatives, e.g., 2-(2-chlorophenylmethylsulfonyl)pyridine N-oxide, useful in preemergence or postemergence control of weeds.

A method of controlling weeds, using substituted 2-sulfinyl or2-sulfonyl pyridine N-oxides disclosed herein, is claimed in ourcopending application Ser. No. 559,188 filed of even date herewith andhereby incorporated herein by reference.

This invention relates to certain substituted 2-sulfinyl and 2-sulfonylpyridine N-oxides.

W. Walter et al., Liebig's Ann., 695, 77 (1966), disclose2-(phenylmethylsulfinyl)pyridine N-oxide (also called2-benzylsulfinylpyridine N-oxide) and 2-(phenylmethylsulfonyl)pyridineN-oxide (also called 2-benzylsulfonylpyridine N-oxide), but no utilityfor these chemicals is disclosed.

U.S. Pat. No. 3,107,994, Rawlings et al., Oct. 22, 1963, disclosescertain herbicidal 2-(alkenylthio) pyridine N-oxides, while U.S. Pat.No. 3,155,671 D'Amico, Nov. 3, 1964, discloses certain herbicidal benzyl2-thiopyridine N-oxides.

The state of the art is further illustrated by such references as E.Shaw et al., JACS 72, 4362 (1950) and U.S. Pat. No. 3,772,307, Kaminskyet al., Nov. 13, 1973.

The present 2-sulfinyl and 2-sulfonyl pyridine N-oxide derivatives makepossible markedly improved results, specifically in herbicidalperformance, over various compounds of the prior art.

Weeds compete with crops for light, moisture, nutrients and space. Thus,weeds inhibit the production of foilage, fruit or seed of agriculturalcrops. The presence of weeds may also reduce the quality of theharvested crop and reduce harvesting efficiency. Weed control isessential for maximum production of many agronomic and horticulturalcrops including soybeans (Glycine max L.) peanuts (Arachis hypogaea L.)flax (Linum usitatissium L.) and cotton (Gossypium sp.).

In accordance with the invention, there are provided new herbicidallyeffective 2-sulfinyl and 2sulfonyl pyridine N-oxides of the formula##SPC1##

Where

N IS 1 OR 2;

R₁ is hydrogen or methyl;

R₂ has one of the following values when R₁ is hydrogen:

2,2-DICHLOROCYCLOPROPYL, 2,2-DICHLORO- 1-METHYLCYCLOPROPYL, CYANO,NAPHTHYL, METHYLNAPHTHYL, MONOSUBSTITUTED PHENYL WHEREIN THE SUBSTITUENTIS IN THE ORTHO POSITION AND IS SELECTED FROM ALKYL HAVING 1 TO 2 CARBONATOMS, HALOGEN, NITRO, OR POLYSUBSTITUTED PHENYL HAVING FROM 2 TO 5SUBSTITUENTS WHICH MAY BE THE SAME OR DIFFERENT AND ARE SELECTED FROMALKYL HAVING 1 OR 2 CARBON ATOMS, HALOGEN, NITRO, METHOXY, ETHOXY, ANDMETHYLENEDIOXY; AND

R₂ has one of the following values when R₁ is methyl:

PHENYL, NAPHTHYL, OR PHENYL SUBSTITUTED WITH 1 TO 3 SUBSTITUENTS WHICHMAY BE THE SAME OR DIFFERENT AND ARE SELECTED FROM ALKYL HAVING 1 TO 2CARBON ATOMS, HALOGEN AND NITRO.

Of particular interest are compounds of the above-defined class in whichR₁ is hydrogen and R₂ is 2-methylphenyl, or di- or tri-substitutedphenyl wherein the substituents are methyl or chlorine.

Also of special value are compounds of the class defined above in whichR₁ is methyl and R₂ is selected from the group consisting of phenyl,phenyl substituted with 1 or 2 methyl groups, monohalophenyl, and2-naphthyl.

Preferred pyridine N-oxide derivatives of the invention include2-(2,5-dimethylphenylmethylsulfonyl) pyridine N-oxide,2-(2,4,6-trimethylphenylmethylsulfonyl) pyridine N-oxide,2-(2,6-dichlorophenylmethylsulfonyl) pyridine N-oxide,2-(2,4-dichlorophenylmethylsulfinyl) pyridine N-oxide,2-(2,6-dichlorophenylmethylsulfinyl) pyridine N-oxide,2-(1-[4-methylphenyl]ethylsulfonyl) pyridine N-oxide,2-(2,3,6-trichlorophenylmethylsulfonyl) pyridine N-oxide,2-(2-methylphenylmethylsulfonyl) pyridine N-oxide,2-(1-[4-fluorophenyl]ethylsulfonyl) pyridine N-oxide,2-(1-[2,5-dimethylphenyl]ethylsulfonyl) pyridine N-oxide,2-(2,3,6-trichlorophenylmethylsulfinyl) pyridine N-oxide,2-(1-phenylethylsulfonyl)pyridine N-oxide,2-(1[2-naphthyl]ethylsulfonyl)pyridine N-oxide, 2-(1-[4-chlorophenyl]ethylsulfonyl)pyridine N-oxide,2-(1-[4-bromophenyl]ethylsulfonyl)pyridine N-oxide,2-(2,3,6-trimethylphenylmethylsulfonyl)pyridine N-oxide, and2-(2,3,6-trimethylphenylmethylsulfinyl)pyridine N-oxide.

Particularly preferred are 2-(2,5dispersing N-oxide,2-(2,6-dichlorophenylmethylsulfinyl)pyridine N-oxide, 2-(1-[2,5-dimethylphenyl]ethylsulfonyl)pyridine N-oxide,2-(2,4,6-trimethylphenylmethylsulfonyl)pyridine N-oxide,2-(1-[2-naphthyl]ethylsulfonyl)pyridine N-oxide,2-(1-[4-chlorophenyl]ethylsulfonyl)pyridine N-oxide,2-(1-[4-methylphenyl]ethylsulfonyl)pyridine N-oxide, and2-(2,3,6-trimethylphenylmethylsulfinyl)pyridine N-oxide. and

The pyridine N-oxide derivatives of the invention are useful for bothpreemergence and postemergence control of weeds, and are furthermoreremarkable for their ability to selectively control weeds without injuryto desirable crops. Excellent control of weeds such as quackgrass[Agropyron repens (L.) Beauv.] from seed, Texas panicum (Panicum texanumBuckl.), giant foxtail (Setaria faberi Herrm.), yellow foxtail [Setarialutescens (Weigel) Hubb.], green foxtail [Setaria viridis (L.) Beauv.],barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and wild oats (Avenafatua L.) can be achieved with such chemicals as2-(2,5-dimethylphenylmethylsulfonyl) pyridine N-oxide, without injury tosuch crops as flax (Linum usitatissimum L.), alfalfa (Medicago sativaL.), cotton (Gossypium sp.), soybeans [Glycine max (L.) Merr.], peanuts(Arachis hypogaea L.), tomatoes (Lycopersicon esculentum Mill.) andtobacco (Nicotiana tabacum L.).

Surprisingly, the herein described 2-sulfinyl and 2-sulfonyl pyridineN-oxides are unexpectedly more effective herbicides than theircorresponding sulfide precursors.

The procedures for using the present 2-sulfinyl and 2-sulfonyl pyridineN-oxide derivatives as herbicides may be in accordance with conventionalagricultural practice. The chemicals are ordinarily applied asformulations containing a carrier and/or surface-active agent. Theformulation may contain more than one of the described pyridine N-oxidederivatives if desired; other active herbicides may be included in theformulation as well.

Thus, the chemical may be impregnated on finely divided or granularinorganic or organic carriers such as attapulgite clay, sand,vermiculite, corn cobs, activated carbon or other granular carriersknown to the art. The impregnated granules may then be spread on thesoil. Furthermore, the chemical may be formulated as a wettable powderby grinding it into a fine powder and mixing it with an inactivepowdered carrier to which a surface active dispersing agent has beenadded. Typical powdered solid carriers are the various mineralsilicates, e.g., mica, talc, pyrophyllite and clays. The wettable powdermay then be dispersed in water and sprayed on the soil surface or weeds.Similarly, an emulsifiable concentrate may be prepared by dissolving thechemical in a solvent such as benzene, toluene, or other aliphatic oraromatic hydrocarbon to which a surface active dispersant agent has beenadded. The emulsifiable concentrate may then be dispersed in water andapplied by spraying. Suitable surface activity agents are well known tothose skilled in the art and reference may be had to McCutcheon'sDetergents and Emulsifiers, 1970, Allured Publishing Corp., Ridgewood,New Jersey; or Hoffman et al. U.S. Pat. Nos. 2,614,916, cols. 2 to 4 and2,547,724, cols. 3 to 4, for example of appropriate surface activeagents. The concentration of active chemical in the formulation may varywidely, e.g., from 1 to 95%. The concentration of active chemical indispersions applied to the soil or foliage is almost invariably from0.002% to 75%. The chemical is frequently applied at rates of 0.10 to 25pounds per acre. For use as a preemergence herbicide, the chemical isapplied to soil which contains weed and crop seed (either to the surfaceof the soil or incorporated into the upper one to three inches of soil).

The most suitable rate of application in any given case will depend onsuch factors as soil type, soil pH, soil organic matter content, thequantity and intensity of rainfall before and after treatment, the airand soil temperature, light intensity and light duration per day. All ofthese factors can have an influence on the efficacy of the chemicals foruse as herbicides.

The herbicidal use may include selective weed control in crops such assoybeans, cotton, flax and peanuts.

The 2-sulfinyl and 2-sulfonyl pyridine N-oxide derivatives of theinvention may be prepared from known compounds (see A. R. Katritsky, J.Chem. Soc., 191 [1957], U.S. Pat. Nos. 3,107,994 and 3,155,671 referredto above, and the E. Shaw et al. and W. Water et al. articles referredto above). The parent 2-thiopyridine N-oxides are prepared by either oftwo procedures: (1) the reaction of 2-chloropyridine N-oxide with theappropriate mercaptan in the presence of an acid acceptor such as analkaline earth hydroxide; (2) reaction of the sodium salt of2-mercaptopyridine N-oxide with a suitable halide preferentially of thebenzyl type but not limited to. The yields of the two procedures arecomparable.

An alternate and useful synthetic route involves the oxidation of a2-thiopyridine prepared by methods described in the literature. Theoxidation involves the conversion of both the sulfur and nitrogen totheir higher oxidative states in a single preparative step. In this casethe products are sulfones as the sequence of oxidation proceeds fromsulfide → sulfoxide → sulfone → sulfone N-oxide. The oxidant mostgenerally employed, but not limited to, is 30 - 50% hydrogen peroxide inglacial acetic acid. In excess of three equivalents of peroxide isnecessary.

The conversion of the 2-thiopyridine N-oxide to analagous sulfinyl orsulfonyl compound is accomplished by employing one or two equivalents ofan oxidizing agent selected from, but not necessarily limited to,hydrogen peroxide, peracetic acid, and the aromatic peroxy acids. Theratio of peroxide to substrate varies with the desired product. Ageneral outline of routes and equivalents involved can be depicted asfollows: ##SPC2##

The solvents employed vary with the oxidant as described in theliterature (Katritsky and Lagowski, Chemistry of the HeterocyclicN-Oxides, Academic Press, 1971). Glacial acetic acid and water arepreferred when hydrogen peroxide is used and a nonpolar solvent such aschloroform with the aromatic peroxy acids. When water is employed as asolvent a catalyst of the nature of a tungsten, vanadium, zirconium ormolybdenum salt (U.S. Pats. Nos. 3,005,852, Freyermuth et al., Oct. 24,1961, 3,006,962, Schutz et al., Oct. 31, 1961, 3,006,963, Buc et al,Oct. 31, 1961 and British Pat. No. 1,335,626, Eastman Kodak Co., Oct.31, 1973) is generally used. Temperature and time are a function of thesulfide employed with the range varying from 50° to reflux in the caseof water and acetic acid to 0° to 60° with chloroform.

Compounds of the invention may be used for selective control of variousgrasses and broadleaved weeds including pigweed (Amaranthus retroflexusL.) and purslane (Portulaca oleracea L.) in diverse crops including flax(Linum usitatissimum L.), alfalfa (Medicago sativa L.), cotton(Gossypium sp.), soybeans [Glycine max (L.) Merr.], peanuts (Arachishypogaea L.), tomatoes (Lycopersicon esculentum Mill.) and tobacco(Nicotiana tabacum L.). Application may be in aqueous solutions orsuspensions which may be sprayed onto the soil surface prior to weed andcrop emergence and before or after the crop seed is sown. The soil mayreceive a shallow tilling (less than 3 inches) after application of thechemical, but this is not required as it is with some preemergenceherbicides. The compounds of this invention may also be applied bybroadcast of a granular formulation prior to weed and crop emergence.

Various weeds such as crabgrass [Digitaria ischaemum (Schreb.) Muhl.]may be controlled by postemergence application of compounds of thisinvention.

Compounds of this invention may be added as a "tank mix" to otherherbicide solutions so that the number of different weed speciescontrolled in a single application will be increased. The formulationsof invention compounds may also include other herbicides so that thespectrum of weeds controlled by spray or granular application may beincreased.

The following examples will serve to illustrate the practice of theinvention in more detail. The examples summarized in Table I illustratepreparation of chemicals of the invention while subsequent examplesillustrate control of weeds with the chemicals. In the examples themelting points are uncorrected. In Table I, the symbol IR in theAnalysis column indicates that infrared data for the compound are givenin Table II. The infrared data were obtained on a Perkin-Elmer Infracord(trademark). In the examples illustrating use of the chemicals, eachchemical is identified by the example number assigned to the chemical inTable I.

EXAMPLE 1 2-(2,5-Dimethylphenylmethylsulfonyl) pyridine N-oxide

To a stirred solution of 792 gms (2.2 mole) (40% aqueous solution)2-mercaptopyridine N-oxide, sodium salt in 1400 ml of ethanol is added344 gms (2.2 mole) 2,5-dimethylbenzylchloride over a period of 15minutes. The mixture is brought to reflux for 15 minutes, filtered hot,and treated with 5 liters of cold water. The product is filtered off andoven dried to 533 gms of 2-(2,5-dimethylphenylmethylthio)pyridineN-oxide. Yield 97%. Melting point 140° - 142°C.

A. To a vigorously stirred solution of 74 gms (0.3 mole) of the thiocompound in 250 ml of glacial acetic acid at 45° - 50°C. is added 75 mlof 30% hydrogen peroxide over a period of 15 minutes. The temperature israised to 70°C. and after 30 minutes increased again to 80° - 90° andheld for 3 hours. The reaction mixture is lowered to ambient temperatureand added slowly to two to 3 times its volume of vigorously agitatedcold water. The pale yellow solid separates and is filtered off.Recrystallizes from ethanol to yield 74.5 gms of fine crystals meltingat 156° - 158°C. (IR N-O 1275 cm.sup.⁻¹ SO₂ 1140, 1315 cm.sup.⁻¹). Yield89% theory.

Analysis: Calc. for C₁₅ H₁₅ NO₃ S. C, 60.63; H, 5.45; N, 5.05; S, 11.54.Found: C, 60.66; H, 5.56; N, 5.18; S, 11.81.

B. To a heated (80° - 90°) vigorously stirred slurry of 30 gms (0.12mole of thio compound in 150 ml of water containing 10 gms of aceticacid and 0.2 gms of sodium tungstate dihydrate is slowly added 26 ml of30% hydrogen peroxide. The addition is exothermic and the temperature ismaintained at 80° - 90°C. for the first 14 ml then allowing it to riseto the 95° - 105°C. range for the remaining 12 ml.

The initial slurry becomes quite thin at the sulfoxide stage and againseparating at the sulfone stage. Overall reaction time is about onehour. The reaction mixture is filtered, washed with water and air dried.Melting point 156° - 158°C. Mixed m.p. with authentic sample shows nodepression. Yield 32.8 gms (quantitative).

EXAMPLE 2 2-(2,4,6-Trimethylphenylmethylsulfonyl)pyridine N-oxide

A mixture of 17 gms (0.05 mole) 2-mercaptopyridine N-oxide, sodium salt(40% aqueous solution) and 8.5 gms (0.05 mole) α ² chloroisodurene in 50ml of ethanol is brought to reflux for 15 minutes. The volatiles areremoved and the residue extracted with 150 ml of boiling chloroform,filtered and dried over sodium sulfate. Evaporation and trituration ofthe residue with a few drops of acetone induced crystallization. A yieldof 11.5 gms of 2-(2,4,6-trimethylphenylmethylthio)pyridine N-oxide isobtained. Melting point 137° - 138°C. Structure confirmed by IR and NMR.

To a well cooled (0° - 10°C.) solution of 15 gms (0.06 mole) of thiocompound in 200 ml of chloroform is slowly added with vigorous stirring25 gms (0.12 mole) meta chloroperoxybenzoic acid (MCPBA) (85%) in 400 mlof chloroform. Upon completion of the addition the temperature ispermitted to rise to ambient and stirring is continued 24 hours. Thereaction mixture is washed thoroughly with 300 ml of saturated sodiumbicarbonate solution and water then dried over magnesium sulfate.Evaporation of the chloroform, and crystallization of the solid residuefrom methanol yields 15 grams (86% theory) of product. Melting point173° - 175° (IR N-O 1275 cm.sup.⁻¹, SO₂ 1310, 1140 cm.sup.⁻¹).

Analysis: Calc. for C₁₅ H₁₇ NO₃ S. C, 61.90; H, 5.84; N, 4.81. Found: C,61.97; H, 6.06; N, 4.79.

EXAMPLE 3 2-(2,6-Dichlorophenylmethylsulfinyl)-pyridine N-oxide

A mixture of 37 gms (0.1 mole) 2-mercaptopyridine N-oxide, sodium salt(40% aqueous solution) and 19.5 gms (0.1 mole)2,6-dichlorobenzylchloride in 200 ml of ethanol is warmed to 65° - 70°for 30 minutes, cooled and filtered. The filter cake is washedthoroughly water and finally with 40 ml of acetone. The dry cake (25.3gms) represents a 92% yield of 2-(2,6-dichlorophenylmethylthio)pyridineN-oxide. Melting point 240° - 241°C. Structure confirmed by IR and NMR.

A solution of 5.8 gms (0.02 mole) of thio compound in 100 ml ofchloroform is cooled to 0° - 10°C. Four (4) gms (0.02 mole) MCPBA (85%)is added with good stirring. After twenty-four hours at ambienttemperature the reaction mixture is washed thoroughly with sodiumbicarbonate solution, dried and evaporated. Crystallization from hotethyl acetate yielded 4.3 gms (71% theory) of product. Melting point135° - 137°C. (IR N-O 1260 cm.sup.⁻¹ SO 1050 cm.sup.⁻¹).

Analysis: Calc. for C₁₂ H₉ Cl₂ NO₂ S. C, 47.65; H, 2.98; N, 4.64. FoundC, 47.25; H, 2.95; N, 4.29.

EXAMPLE 4 2-(1-[4-Chlorophenyl]ethylsulfonyl)pyridine N-oxide

The intermediate 2(-1-[4-chlorophenyl]ethylthio)pyridine N-oxide wasprepared from 1-(4-chlorophenyl)ethylchloride and 2-mercaptopyridineN-oxide, sodium salt by the procedure described in Example 2. Meltingpoint 106° - 108°C. Structure confirmed by IR and NMR.

The thio compound (0.01 mole) is oxidized with MCPBA (0.04 mole) andisolated in the manner previously described in Example 2. Yield 78%theory. Melting point 188° - 191°C. (IR N-O 1300 cm.sup.⁻¹ SO₂ 1340,1160 cm.sup.⁻¹).

Analysis: Calc. for C₁₃ H₁₂ ClNO₃ S. C, 52.44; H, 4.06; N, 4.71. FoundC, 52.09; H, 4.11; N, 4.61.

EXAMPLE 5 2-(1-[4-methylphenyl]ethylsulfonyl)-pyridine N-oxide

The intermediate compound 2-(1-[4-methylphenyl]-ethylthiol)pyridineN-oxide is prepared from 1-(4-methylphenyl)ethyl chloride and2-mercaptopyridine N-oxide, sodium salt by the procedure described inExample 2. Melting point 83° - 85°C. Structure confirmed by IR and NMR.

The thio compound (0.02 mole) is oxidized with MCPBA (0.04 mole) andisolated in the manner described in Example 2. (IR N-O 1275 cm.sup.⁻¹SO₂ 1315, 1140 cm.sup.⁻¹).

Analysis: Calc. for C₁₄ H₁₅ NO₃ S. C, 60.35; H, 5.45; N, 5.02. Found C,61.18; H, 5.70; N, 5.22.

EXAMPLE 6 2-(1-[2,5-Dimethylphenyl]ethylsulfonyl)pyridine N-oxide

The intermediate 2-(1-[2,5-dimethylphenyl]-ethylthio)pyridine N-oxide isprepared from 1-(2,5-dimethylphenyl)ethyl chloride and2-mercaptopyridine N-oxide, sodium salt by the procedure described inExample 2. Melting point 118° - 120°C. Structure confirmed by IR andNMR.

The thio compound (0.05 mole) is oxidized with MCPBA (0.1 mole) andisolated in the manner described in Example 2. Yield 83% theory. Meltingpoint 160° - 163°C. (IR N-O 1275 cm.sup.⁻¹, SO₂ 1315, 1145 cm.sup.⁻¹).

EXAMPLE 7 2-(1-[2-Naphthyl]ethylsulfonyl)-pyridine N-oxide.

The intermediate 2-(1-[2-naphthyl]ethylthio)-pyridine N-oxide isprepared from 1-(2-naphthyl)ethyl chloride and 2mercapto pyridineN-oxide, sodium salt by the procedure described in Example 2. Meltingpoint 112° - 115°C. Structure confirmed by IR and NMR.

The thio compound (0.02 mole) is oxidized with MCPBA (0.04 mole) andisolated in the manner described in Example 2. Crystallization fromethanol yielded 73% product. Melting point 144° - 146°C. (IR N-O 1275cm.sup.⁻¹, SO₂ 1310, 1140 cm.sup.⁻¹).

EXAMPLE 8 2-(2,3,6-Trimethylphenylmethylsulfinyl)pyridine N-oxide

The intermediate 2-(2,3,6-trimethylphenylmethylthio)pyridine N-oxide isprepared from α² -bromoprehnitene with 2-mercaptopyridine N-oxide,sodium salt by the procedure described in Example 2. Yield 50% theory.Melting point 108° - 110°C. Structure confirmed by IR and NMR.

The thio compound (0.03 mole) is oxidized with MCPBA (0.03 mole) andisolated in the manner described in Example 2. Yield 50% theory. Meltingpoint 72° - 75°C. (IR N-O 1250 cm.sup.⁻¹, SO 1050 cm.sup.⁻¹).

EXAMPLE 9 2-(1-Phenylethylsulfonyl)pyridine N-oxide

To a well stirred, cold (0° - 10°) solution of 46.3 gms (0.2 mole) of2-(1-phenylethylthio)pyridine N-oxide in 400 ml of chloroform is slowlyadded a solution of 80 gms (0.4 mole) MCPBA in one liter of chloroform.After three hours at 0° - 10° the temperature was allowed to becomeambient and stand for twenty-four hours. After washing with saturatedsodium bicarbonate to remove all traces of acid the chloroform solutionwas dried and evaporated. Yield 47 gms (90% theory). Melting point141° - 143°C. (IR N-O 1260 cm.sup.⁻¹, SO₂ 1300, 1140 cm.sup.⁻¹).

Analysis: Calc. for C₁₃ H₁₃ NO₃ S. C, 59.40; H, 4.95; N, 5.32. Found C,59.03; H, 4.90; N, 5.35.

EXAMPLE 10 2-(2,4-Dichlorophenylmethylsulfinyl)-pyridine N-oxide

A well stirred solution of 5.8 gms (0.02 mole) of2-(2,4-dichlorophenylmethylthio)pyridine N-oxide in 50 ml of chloroformis treated at 0° - 10° with 4 gms (0.02 mole) MCPBA (85%) in 50 ml ofchloroform. The mixture is allowed to rise to ambient and held for 16hours. The reaction mixture is washed with saturated sodium bicarbonate,dried and evaporated to 5.5 gms (89% theory) of product. Melting point138° - 141°C. Structure confirmed by IR and NMR. (IR N-O 1240 cm.sup.⁻¹,SO 1050 cm.sup.⁻¹).

EXAMPLE 11 2-(2-Methylphenylmethylsulfonyl)-pyridine N-oxide

The intermediate 2-(2-methylphenylmethylthio)-pyridine N-oxide isprepared by the procedure described in Example 2 from α -chloro o-xyleneand 2-mercaptopyridine N-oxide sodium salt. Melting point 134° - 136°C.Yield 85% theory. Structure confirmed by IR and NMR.

A slurry of 14 gms (0.06 mole) thio compound, 100 ml water, 0.5 gmssodium tungstate dihydrate, and 4 ml of glacial acetic acid is heated to75°C. Twelve ml hydrogen peroxide (30%) (0.12 mole) is added portionwiseand with only a slight exotherm until 6 ml is consumed. The remaining 6ml is added at steam bath temperature in three 2 ml portions at a ratecontrolled by testing the mixture with potassium iodide-starch paper toassure consumption of the previous peroxide. The final temperature was97° after one hour. Cool, filter and wash cake with water and a smallamount of cold ethanol. After drying the product 15.4 gms (99% theory)is obtained. Melting point 159° - 160.5°C. Structure confirmed by IR.

Analysis: Calc. for C₁₃ H₁₃ NO₃ S. C, 59.31; H, 4.98; N, 5.32. Found C,59.30; H, 5.21; N, 5.31.

EXAMPLE 12 2-(2,2-Dichloro-1-methylcyclopropylmethylsulfonyl)pyridineN-oxide

To a well stirred solution of 62.5 gms (0.25 mole)2-(2,2-dichloro-1-methylcyclopropylmethylthio)-pyridine in 250 ml ofglacial acetic acid at ambient temperature 90 gms (0.8 mole) of 30%hydrogen peroxide is slowly added. The temperature is increased to 80°over a period of two hours and held for twelve hours. An additional 10ml of peroxide is added and heating continued for 4 hours.

The reaction mixture was reduced to approximately one-third its volumewith a rotary evaporator and the residue slowly poured into a vigorouslystirred four fold volume of cold water. The separated product isfiltered off and vacuum dried to 31.5 gms. Yield 42% theory. Meltingpoint 93° - 94°C. (IR N-O 1280 cm.sup.⁻¹, SO₂ 1315, 1140 cm.sup.⁻¹).

Analysis: Calc. for C₁₀ H₁₁ Cl₂ NO₃ S. C, 40.50; H, 3.72; Cl, 23.95; N,4.72. Found C, 40.36; H, 3.77; Cl, 24.15; N, 4.63.

EXAMPLE 13 2-(2,3,6-Trichlorophenylmethylsulfinyl)pyridine N-oxide

The intermediate 2-(2,3,6-trichlorophenylmethylthio)pyridine N-oxide isprepared from 2,3,6-trichlorobenzylchloride and 2-mercaptopyridineN-oxide sodium salt by the procedure employed in Example 3. Meltingpoint 232° - 234°C. Yield quantitative. Structure confirmed by IR andNMR.

A slurry of 6.4 gms (0.02 mole) of thio compound in 50 ml of chloroformis cooled to 5° - 10°C. and solution of 4 gms (0.02 mole) MCPBA in 100ml of chloroform is slowly added. The reaction mixture is allowed torise to room temperature, stirred for sixteen hours, washed withsaturated sodium bicarbonate solution and dried over sodium sulfate. Thedry solution is evaporated to dryness and crude product refluxed inethanol, cooled and filtered. Yield of product 65% theory. Melting point168° - 170°C. (IR N-O 1350 cm.sup.⁻¹, SO 1050 cm.sup.⁻¹).

Analysis: Calc. for C₁₂ H₈ Cl₃ NO₂ S. C, 42.82; H, 2.39; N, 4.16; S,9.54. Found C, 42.01; H, 2.32; N, 4.18; S, 9.74.

EXAMPLE 14 2-(2,6-Dichlorophenylmethylsulfonyl)pyridine N-oxide

A mixture of 37 gms (0.1 mole) of (40% solution) 2-mercaptopyridineN-oxide, sodium salt and 19.5 gms (0.1 mole) 2,6-dichlorobenzylchloridein 200 ml ethanol is warmed to 65° for thirty minutes, cooled andfiltered. The filter cake is washed thoroughly with water and finallywith 40 ml of acetone. Vacuum drying of the cake yields 25.3 gms (92%theory) of product, 2-(2,6-dichlorophenylmethylthio)pyridine N-oxide.Melting point 240° - 241°C. Structure confirmed by IR.

A slurry of 29 gms (0.1 mole) of the thio compound in 300 ml ofchloroform at 10° is treated slowly with 40 gms (0.2 mole) MCPBA (85%)in 450 ml of chloroform. The mixture is permitted to rise to ambienttemperature resulting in a clear solution which is held sixteen hours.The solution is washed with saturated sodium bicarbonate solution, driedover magnesium sulfate and evaporated to dryness. The residue isslurried in 400 ml of boiling methanol, cooled and filtered to yield 28gms (89% theory) of product. Melting point 214° - 215.5°C.

Analysis: Calc. for C₁₂ H₉ Cl₂ NO₃ S. C, 45.32; H, 2.83; N, 4.40. FoundC, 45.67; H, 2.89; N, 4.55.

EXAMPLE 15 2-(2,3,6-Trichlorophenylmethylsulfonyl)pyridine N-oxide

The compound 2-(2,3,6-trichlorophenylmethylthio)-pyridine N-oxide isprepared from 2,3,6-trichlorobenzylchloride and 2-mercaptopyridineN-oxide sodium salt by the procedure employed in Example 1. Meltingpoint 232° - 234°C. Yield quantative. Structure confirmed by IR and NMR.

A slurry of 6.4 gms (0.02 mole) of thio compound in 50 ml of chloroformis cooled to 5° - 10°C. and solution of 8 gms (0.04 mole) MCPBA in 100ml of chloroform is slowly added. The reaction mixture is allowed torise to room temperature, stirred for sixteen hours, washed andsaturated sodium bicarbonate solution and dried over sodium sulfate. Thedry solution is evaporated to dryness and crude product refluxed inethanol, cooled and filtered. Yield of product 6.7 gms (95% theory).Melting point 194° - 196°C. Structure confirmed by IR and NMR.

EXAMPLE 16 2-(1-[4-Fluorophenyl]ethylsulfonyl)-pyridine N-oxide

The compound is prepared from 2-mercaptopyridine N-oxide sodium salt and1-(4-fluorophenyl)ethylchloride in the manner described in Example 4.The 2-(1-[4-fluorophenyl]ethylthio)pyridine N-oxide is obtained in 40%yield. Melting point 95° - 97°C. Structure confirmed by IR and NMR.

Oxidation of the thio compound (0.04 mole) with 0.08 mole) MCPBA andisolation procedure are the same as employed in Example 7. Yield 83%.Melting point 142° - 144°C.

Analysis: Calcd. for C₁₃ H₁₂ FNO₃ S. C, 55.50; H, 4.30; N, 4.98. FoundC, 55.47; H, 4.61; N, 5.07.

EXAMPLE 17 2-(1-[4-Bromophenyl]ethylsulfonyl)-pyridine N-oxide.

The compound 2-(1-[4-bromophenyl]ethylthio)-pyridine N-oxide is preparedfrom 1-(4-bromophenyl)-ethylchloride and 2-mercaptopyridine N-oxidesodium salt by the procedure described in Example 1. The melting pointis 113° - 115°C. Structure is confirmed by IR and NMR.

The thio compound (0.05 mole) is oxidized with MCPBA (0.1 mole) andisolated in the manner previously described in Example 9. Yield 85%.Structure confirmed by IR and NMR.

Analysis: Calc. for C₁₃ H₁₂ BrNO₃ S. C, 45.63; H, 3.45; N, 4.09. Found:C, 45.04; H, 3.32; N, 4.15.

In accordance with the same procedure the chemicals listed in Table Imay be prepared. Table I summarizes the foregoing preparations as wellas additional similar preparations; Table II gives infrared data. Thenumbers assigned to the preparations in Table I are used to identify thechemicals in the subsequent examples. Compound 28 in Table I alsocontained a minor amount of the 4-ethylphenyl isomer.

                                      Table I                                     __________________________________________________________________________    Herbicidal Chemicals                                                                                           Analysis-Calc/Found                          Ex          Name           m.p.   C     H    N    S                           __________________________________________________________________________    12 2-(2,2-Dichloro-1-methylcyclopropylmethyl-                                    sulfonyl)pyridine N-oxide                                                                              93-95°                                                                      40.50 3.72 4.73 10.81                                                         40.51 3.87 4.59 10.94                        21 2-(1-Naphthylmethylsulfonyl)pyridine N-oxide                                                          183.186                                                                             IR                                           20 2-(3,4-Dimethylphenylmethylsulfonyl)pyridine                                  N-oxide                 165-167                                                                             60.63 5.45 5.05 11.54                                                         60.77 5.73 5.03 11.71                        1  2-(2,5-Dimethylphenylmethylsulfonyl)pyridine                                  N-oxide                 156-158                                                                             60.63 5.45 5.05 11.54                                                         60.66 5.56 5.18 11.81                        11 2-(2-Methylphenylmethylsulfonyl)pyridine                                      N-oxide                 159-161                                                                             59.31 4.93 5.32                                                               59.30 5.21 5.31                              14 2-(2,6-Dichloromethylsulfonyl)pyridine                                        N-oxide                 214-215                                                                             45.37 2.83 4.40                                                               45.67 2.89 4.55                              2  2-(2,4,6-Trimethylphenylmethylsulfonyl)-                                      pyridine N-oxide        173-175                                                                             61.90 5.84 4.81                                                               61.97 5.06 4.79                              24 2-(2,4-Dichlorophenylmethylsulfonyl)pyridine                                  N-oxide                 154-156                                                                             IR                                           9  2-(1-Phenylethylsulfonyl)pyridine N-oxide                                                             141-143                                                                             59.40 4.95 5.32                                                               59.03 4.90 5.35                              22 2-(2-Chlorophenylmethylsulfonyl)pyridine                                      N-oxide                 151-152                                                                             IR                                           25 2-([2-Methoxy-5-nitrophenyl]methylsulfonyl)-                                  pyridine N-oxide        226-227                                                                             IR                                           27 2-(2-Fluorophenylmethylsulfonyl)pyridine                                      N-oxide                 151-153                                                                             54.00 3.74 5.24                                                               54.03 3.79 5.31                              26 2-([3,4-Dioxymethylene-6-chlorophenyl]-                                       methylsulfonyl)pyridine N-oxide                                                                       179-180                                                                             47.60 3.06 4.28                                                               46.87 2.83 4.23                              28 2-(2-Ethylphenylmethylsulfonyl)pyridine                                       N-oxide                 --    IR                                           4  1-(4-Chlorophenyl)ethylsulfonyl]pyridine                                      N-oxide                 188-191                                                                             IR                                           3  2-(2,6-Dichlorophenylmethylsulfinyl)-                                         pyridine N-oxide        135-137                                                                              47.65                                                                              2.98 4.64                                                               47.25 2.95 4.25                              29 2-(2-5-Dimethylphenylmethylsulfinyl)-                                         pyridine N-oxide        142-144                                                                             64.80 5.64 5.26                                                               64.43 5.67 5.13                              10 2-(2,4-Dichlorophenylmethylsulfinyl)-                                         pyridine N-oxide        138-141                                                                             IR                                           30 2-(2,4,6-Trimethylphenylmethylsulfinyl)-                                      pyridine N-oxide        164-166                                                                             65.50 6.18 5.09                                                               66.11 6.49 5.15                              31 2-(2-Chlorophenylmethylsulfinyl)pyridine                                      N-oxide                 124-127                                                                             53.65 3.73 5.22                                                               53.91 4.11 5.25                              32 2-(3,4-Dimethylphenylmethylsulfinyl)                                          pyridine N-oxide        123-126                                                                             64.43 5.75 5.36                                                               64.89 6.08 5.40                              33 2-(2-Methylphenylmethylsulfinyl)pyridine                                      N-oxide                  99-102                                                                             63.14 5.30 5.66 12.96                                                         62.66 5.31 5.45 12.57                        23 2-Cyanomethylsulfinyl pyridine N-oxide                                                                164-165                                                                             IR                                           34 2-(2-Fluorophenylmethylsulfinyl)pyridine                                      N-oxide                 110-113                                                                             57.40 3.98 5.57                                                               57.43 3.95 5.68                              35 2-(2-Methoxy-5-methylphenylmethylsulfonyl)-                                   pyridine N-oxide        115-118                                                                             IR                                           36 2-(2-Bromo-5-methoxyphenylmethylsulfonyl)-                                                            157-158                                                                             IR                                           37 2-(Pentachlorophenylmethylsulfonyl)pyridine                                   N-oxide                 235-238                                                                             IR                                           15 2-(2,3,6-Trichlorophenylmethylsulfonyl)-                                      pyridine N-oxide        194-196                                                                             IR                                           7  2-[1-(2-Naphthyl)ethylsulfonyl]pyridine                                       N-oxide                 144-146                                                                             IR                                           5  2-[1-(4-Methylphenyl)ethylsulfonyl]pyridine                                   N-oxide                 158-160                                                                             60.35 5.45 5.05                                                               61.18 5.70 5.22                              16 2-[1-(4-Fluorophenyl)ethylsulfonyl]-                                          pyridine N-oxide        142-144                                                                             55.50 4.30 4.98                                                               55.47 4.61 5.07                              6  2-[1-(2,5-Dimethylphenyl)ethylsulfonyl]-                                      pyridine N-oxide        160-163                                                                             IR                                           17 2-[1-(4-Bromophenyl)ethylsulfonyl]-                                           pyridine N-oxide        193-195                                                                             45.63 3.45 4.09                                                               45.04 3.32 4.15                              42 2-(3,4-Dichlorophenylmethylsulfonyl)pyridine                                  N-oxide                 170-173                                                                             45.30 2.85 4.40                                                               45.20 2.41 4.49                              38 2-(Pentachlorophenylmethylsulfinyl)-                                          pyridine N-oxide        213-215                                                                             IR                                           13 2-(2,3,6-Trichlorophenylmethylsulfinyl)-                                      pyridine N-oxide        168-170                                                                             IR                                           40 2-[1-(4-Fluorophenyl)ethylsulfinyl]-                                          pyridine N-oxide         98-101                                                                             58.85 4.56 5.28                                                               54.94 5.08 5.34                              39 2-[1-(4-Methylphenyl)ethylsulfinyl]pyridine                                   N-oxide                 121-123                                                                             IR                                           19 2-(2,2-Dichlorocyclopropylmethylsulfinyl)-                                    pyridine N-oxide        oil   IR                                           41 2-[1-(4-Bromophenyl)ethylsulfinyl]pyridine                                    N-oxide                 177-180                                                                             IR                                           43 2-(3,4-Dichlorophenylmethylsulfinyl)-                                         pyridine N-oxide        133-135                                                                             47.70 3.00 4.64                                                               47.44 2.92 4.71                              44 2-(1-[3,4-Dichlorophenyl]ethylsulfonyl)-                                      pyridine N-oxide        129-134                                                                             IR                                           46 2-(3,4-Methylenedioxyphenylmethylsulfonyl)-                                   pyridine N-oxide        163-165                                                                             IR                                           18 2-(2,3,6-Trimethylphenylmethylsulfonyl)-                                      pyridine N-oxide        155   IR                                           45 2-(3,4-Methylenedioxyphenylmethylsulfinyl)-                                   pyridine N-oxide        171-173                                                                             IR                                           49 2-(2-Nitrophenylmethylsulfinyl)pyridine                                       N-oxide                 165-167                                                                             IR                                           8  2-(2,3,6-Trimethylphenylmethylsulfinyl)-                                      pyridine N-oxide        72-75 IR                                           51 2-(2-Methyl-1-naphthylmethylsulfinyl)-                                        pyridine N-oxide        127-130                                                                             IR                                           53 2-(2-Iodophenylmethylsulfinyl)pyridine                                        N-oxide                 160-163                                                                             IR                                           56 2-(1-[1-Naphthyl]ethylsulfinyl)pyridine                                       N-oxide                 146-147                                            48 2-(2-Nitrophenylmethylsulfonyl)pyridine                                       N-oxide                 155-158                                                                             IR                                           47 2-(1-[ 2,4,6-Trimethylphenyl]ethylsulfonyl)-                                  pyridine N-oxide        172-175                                                                             IR                                           50 2-(2-Methyl-1-naphthylmethylsulfonyl)-                                        pyridine N-oxide        195-198 IR                                         52 2-(2-Iodophenylmethylsulfonyl)pyridine                                        N-oxide                 142-146                                                                             IR                                           54 2-(1-[4-Nitrophenyl]ethylsulfonyl)pyridine                                    N-oxide                 167-121                                                                             IR                                           55 2-(1-[1-Naphthyl]ethylsulfonyl)pyridine                                       N-oxide                 wax   IR                                           57 2-(3,4-Dimethoxyphenylmethylsulfinyl)-                                                                133-135                                                                             IR                                              pyridine N-oxide                                                           58 2-(3,4-Dimethoxyphenylmethylsulfonyl)-                                        pyridine N-oxide        159-161                                                                             IR                                           59 2-(1[2,5-Diethylphenyl]ethylsulfonyl)-                                                                124-127                                                                             IR                                              pyridine N-oxide                                                           60 2-(2,5-Dimethoxyphenylmethylsulfonyl)-                                        pyridine N-oxide        129-132                                                                             IR                                           61 2-(2,5-Dimethoxyphenylmethylsulfinyl)-                                        pyridine N-oxide        136-138                                                                             IR                                           __________________________________________________________________________

                  Table II                                                        ______________________________________                                        Infrared Data                                                                 Ex       Major Bands (cm.sup.-.sup.1)                                                 SO.sub.n                                                                              n             N-oxide                                         ______________________________________                                        12       1315, 1140 2             1280, 844                                   21       1320, 1155 2             1280, 845                                   20       1310, 1140 2             1270, 840                                   1        1310, 1130 2             1270, 835                                   11       1310, 1130 2             1270, 840                                   14       1320, 1120 2             1240, 840                                   2        1310, 1140 2             1275, 840                                   24       1310, 1140 2             1280, 840                                   9        1300, 1140 2             1260, 840                                   22       1320, 1160 2             1275, 835                                   25       1320, 1140 2             1275, 835                                   27       1310, 1120 2             1270, 840                                   26       1320, 1140 2             1280, 840                                   28       1320, 1150 2             1270, 840                                   4        1340, 1160 2             1300, 850                                   3        1050       1             1260, 840                                   29       1055       1             1260, 830                                   10       1050       1             1240, 840                                   30       1050       1             1255, 840                                   31       1050       1             1260, 845                                   32       1055       1             1260, 840                                   33       1060       1             1260, 845                                   23       1050       1             1240, 845                                   34       1065       1             1270, 850                                   35       1310, 1140 2             1260, 840                                   36       1320, 1140 2             1260, 845                                   37       1330, 1130 2             1280, 850                                   15       1325, 1125 2             1240, 850                                   7        1310, 1140 2             1275, 855                                   5        1315, 1140 2             1275, 845                                   16       1310, 1140 2             1280, 840                                   6        1315, 1145 2             1275, 845                                   17       1310, 1140 2             1275, 845                                   42       1335, 1150 2             1280, 850                                   38       1050       1             1260, 840                                   13       1040       1             1260, 825                                   40       1025       1             1245, 840                                   39       1030       1             1240, 840                                   19       1050       1             1260, 840                                   41       1055       1             1250, 840                                   43       1045       1             1250, 840                                   44       1320, 1140 2             1280, 845                                   46       1310, 1120 2             1250, 845                                   18       1315, 1150 2             1275, 845                                   45       1040       1             1260, 820                                   48       1330, 1140 2             1280, 845                                   47       1310, 1140 2             1270, 845                                   50       1320, 1130 2             1260, 840                                   52       1320, 1130 2             1230, 840                                   54       1320, 1140 2             1270, 845                                   55       1310, 1140 2             1280, 845                                   49       1050       1             1250, 840                                   8        1045       1             1250, 840                                   51       1040       1             1240, 835                                   53       1040       1             1250, 835                                   56       1050       1             1240, 840                                   57       1040       1             1250, 840                                   58       1140, 1320 2             1260, 845                                   59       1145, 1320 2             1280, 845                                   60       1130, 1315 2             1230, 845                                   61       1040       1             1230, 840                                   ______________________________________                                    

EXAMPLE 62

To illustrate effectiveness of the described 2-sulfinyl and sulfonylpyridine N-oxides as preemergent herbicides, 600 mg chemical isdissolved in 10 ml organic solvent (e.g., acetone) to which 30 mgconventional emulsifying agent (e.g., isooctyl polyethyoxyethanol,"Triton X100" [trademark]) is added. The solution is diluted to 100 mlwith distilled water. Twenty milliliters of this 6000 ppm solution isdiluted to 250 ppm with distilled water. The chemical applied at therate of 10 lbs/A (pound per acre) by drenching 46 ml of the 250 ppmsolution on the surface of soil in 41/2 inch diameter plastic pots whichhad been sown with the following weed seeds: rough pigweed (Amaranthusretroflexus L.), purslane (Portulaca oleracea L.) or jimsonweed (Daturastramonium L.), tall morningglory (Ipomea purpurea(L.)Roth), crabgrass(Digitaria ischaemum (Schreb.) Muhl.), barnyardgrass (Echinochloacrusgalli (L.)Beauv.) and giant foxtail (Setaria faberi Herrm.). Thepercent control of the weeds compared to untreated checks is determinedtwo weeks after treatment. Table III shows the results with thepreemergence herbicides of the invention prepared in accordance with theabove examples.

                  Table III                                                       ______________________________________                                        Herbicide activity of 2-sulfinyl                                              and 2-sulfonyl pyridine N-oxides                                              Percent Weed Control                                                                       Purslane.sup.P                                                                or        Tall   Barn-                                                        Jimson    Morning-                                                                             yard  Crab- Giant                               Ex  Pigweed  Weed      glory  grass grass Foxtail                             ______________________________________                                        19  50       O.sup.P   15     100   100   100                                 12  15       90.sup.P  0      95    100   100                                 20  100      10        90     100   100   100                                 21  100      100       5      98    100   100                                 1   100      100       100    100   100   100                                 22  100      0         0      100   100   100                                 11  85       80        25     98    100   100                                 23  95       95        20     90     95    95                                 2   100      0         20     95    100   100                                 14  100      80        80     95    100   100                                 24  100      20        0      95    100   100                                 9   100      100       95     95    100   100                                 25  98       0         0      98     98    95                                 3   100      0         94     100   100   100                                 26  100      0         0      95    100   100                                 27  100      70        0      90    100   100                                 28  100      0         0      98    100   100                                 29  100      0         20     98    100   100                                 10  98       40        70     100   100   100                                 30  100      0         50     98     98   100                                 31  100      25        40     98     98    98                                 32  100      20        0      95     98    98                                 33  100      0         85     98     98   100                                 34  100      0         50     95     98   100                                 4   100      25        0      100   100   100                                 35  100      0         0      100   100   100                                 36  100      0         0      100   100   100                                 37  95       --        --     60     50    30                                 38  100      0         0      100   100   100                                 15  100      100       15     100   100   100                                 13  100      75        100    100   100   100                                 5   95       0         50     98     98    98                                 39  --       --        --     100   100   100                                 16  100      85        98     100   100   100                                 6   95       80        95     100   100   100                                 40  --       25        0      100   100   100                                 7   --       35        0      100   100   100                                 41  0        0         0      98    100   100                                 17  0        0         0      98    100   100                                 42  0        0         0      50     75   100                                 43  100      0         0      100   100   100                                 44  100      100       0      100   100   100                                 45  100      0         0      98    100   100                                 46  100      0         0      100   100   100                                 18  100      30        100    100   100   100                                 47  100      95        75     98     98    98                                 48  100      95        65     98     98    98                                 49  100      60        85     100   100   100                                 8   100      0         100    100   100   100                                 50  100      0         0      95    100   100                                 51  100      0         0      100   100   100                                 52  100      0         0      100   100   100                                 53  100      0         50     100   100   100                                 54  100      0         0      100   100   100                                 55  100      100       100    100   100   100                                 56  30       30        0      30     20    20                                 57  100      --        0      95    100    95                                 58  100      --        0      95     98    98                                 59  0        --        95     50     95    95                                 60  90       0         62     95     95    95                                 61  20       0         0      80     80    80                                 ______________________________________                                    

EXAMPLE 63

Selectively of a herbicide is desirable since it allows control of weedsgrowing among desirable crop plants. To illustrate the usefulness of thecompounds of this invention as selective preemergence herbicides, 0.8 gchemical is dissolved in 50 ml organic solvent such as acetonecontaining 25 mg conventional emulsifying agent (e.g., isoctylpolyethoxyethanol Triton X-100), and sprayed at the rate of 4 lbs.active in 30 gallons of water per acre onto the surface of soilcontained in 15 × 20 in. flats. Weed and crop seeds were sown into thesoil prior to treatment. The percent weed control and crop injury wereevaluated three weeks after treatment. Table IV illustrates theusefulness of these chemicals as selective preemergence herbicides.

                  TABLE VI                                                        ______________________________________                                        Selective Preemergence Herbicide Test                                         ______________________________________                                        Percent Crop Injury                                                           Ex.   Flax    Alfalfa    Cotton                                                                              Soybean  Peanuts                               ______________________________________                                        1     0       10         0     0        0                                     14    0        0         0     0        0                                     9     50      10         0     75       0                                     ______________________________________                                        Percent Weed Control                                                                                                     Barn-                                                     Wild  Texas   Giant yard                               Ex.  Pigweed  Purslane Oats  Panicum Foxtail                                                                             grass                              ______________________________________                                         1   98       100      100   100     100   100                                14   70       100      100   100     100   100                                 9   100      100      100   100     100   100                                ______________________________________                                    

EXAMPLE 64

To illustrate efficacy at 2 lb/A, 50 ppm solutions (Example 64) weredrenched onto the soil surface at the rate of 46 ml per 41/2 inchdiameter pot. The seeds of several weed species were sown into the soilof each pot prior to chemical application. The percent control of weedscompared to untreated checks was determined two weeks after emergence.Table V shows the results of efficacy tests at 2 lb/A.

                  TABLE V                                                         ______________________________________                                        Herbicide Activity at 2 Pounds Per Acre                                                Percent Weed Control                                                                Barn-  Yellow     Green      Texas                                  State of  yard   Fox-  Crab-                                                                              Fox-  Wild or Fall                           Ex.  Oxidation grass  tail  grass                                                                              tail  Oats Panicum                           ______________________________________                                        32   Sulfoxide  90     90    80   50    0   100                               20   Sulfone   100    100    90   75   100  100                               29   Sulfoxide 100    100   100  100   90   100                                1   Sulfone   100    100   100  100   100  100                               33   Sulfoxide  95     95    95   95    0   100                               11   Sulfone   100    100   100  100   95   100                               30   Sulfoxide 100    100   100  95    50   100                                2   Sulfone   100    100   100  100   85   100                               ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        Herbicide Activity at 1/2 lb/A                                                         Percent Weed Control                                                                Barn-  Yellow     Green      Texas                                  State of  yard   Fox-  Crab-                                                                              Fox-  Wild or Fall                           Ex.  Oxidation grass  tail  grass                                                                              tail  Oats Panicum                           ______________________________________                                        31   Sulfoxide 90      80    85  40     0   100                               22   Sulfone   90      95   100  50    30   100                                3   Sulfoxide 100    100   100  100   90   100                               14   Sulfone   100    100   100  95    60   100                               10   Sulfoxide 95     100   100  85    20   100                               24   Sulfone   95     100    85  80    50   100                               ______________________________________                                    

EXAMPLE 65

Listed below are non--limiting examples of formulations which can beused in this invention.

    ______________________________________                                        1.  9.6% active one lb/gallon emulsifiable con-                                   centrate                                                                  a.   2-(2,5-Dimethylphenylmethylsulfonyl)-                                         pyridine N-oxide         0.6 gm                                          b.   Blend of oil soluble sulfonates with                                          polyoxyethylene ethers (Emcol N39-BU                                          [trademark] Witco Chemical Corp.;                                             e.g., nonylphenol polyoxyethylene plus                                        calcium dodecylbenzene sulfonate)                                                                      0.55 gm                                         c.   Chloroform               2.4 gm                                          d.   Benzaldehyde             2.7 gm                                          2.  11.3% active one lb/gallon soluble con-                                       centrate                                                                  a.   2-(Phenylethylsulfonyl)pyridine N-                                            oxide                    24.0 gm                                         b.   Blend of oil soluble sulfonates with                                          polyoxyethylene ethers (Emcol N5003                                           [trademark] Witco Chemical Corp.;                                             e.g., sodium lignin sulfonate plus                                            polycondensate of ethylene oxide, pro-                                        pylene oxide and propylene glycol)                                                                     12.0 gm                                         c.   Phenol (90% aqueous solution                                                                           178.5 gm                                        3.  50% active wettable powder                                                a.   2-(2,5-Dimethylphenylmethylsulfonyl)-                                         pyridine N-oxide         300 gm                                          b.   Alkylaryl polyether alcohol OPE                                               (octylphenoxy polyethoxy ethanol)                                             9-10 units (Triton X-120 [trade-                                              mark], Rohm & Haas)      6 gm                                            c.   Sodium N-methyl-N-palmitoyl taurate                                           (Igepon TN-74 [trademark] GAF Corp.)                                                                   6 gm                                            d.   Polymerized sodium salts of alkyl                                             naphthalene sulfonic acid (Daxad 11                                           [trademark] Dewey & Almy Chemical                                             Company)                 12 gm                                           e.   Kaolinite clay (Dixie Clay [trade-                                            mark])                   84 gm                                           f.   Hydrated amorphous silica (Hi Sil                                             233 [trademark])         192 gm                                          4.  5% active granule                                                         a.   2-(2,5-Dimethylphenylmethyl-                                                  sulfonyl)pyridine N-oxide                                                                              1.0 gm                                          b.   Methylene chloride       9.0 gm                                          c.   Above solution sprayed onto                                                   hydrated magnesium aluminum                                                   Silicate 25/50 mesh (Attaclay                                                 [trademark])             19.0 gm                                         ______________________________________                                    

We claim:
 1. A 2-sulfinyl or 2-sulfonyl pyridine N-oxide compound of theformula: ##SPC3##where n is 1 or 2; R₁ is hydrogen or methyl; R₂ has oneof the following values when R₁ is hydrogen; 2,2-dichlorocyclopropyl,2,2-dichloro-1-methylcyclopropyl, cyano, naphthyl, methylnaphthyl,monosubstituted phenyl wherein the substituent is in the ortho positionand is selected from alkyl having 1 to 2 carbon atoms, halogen, nitro,or polysubstituted phenyl having from 2 to 5 substituents which may bethe same or different and are selected from alkyl having 1 or 2 carbonatoms, halogen, nitro, methoxy, ethyoxy and methylenedioxy; and R₂ hasone of the following values when R₁ is methyl: phenyl, naphthyl, orphenyl substituted with 1 to 3 substituents which may be the same ordifferent and are selected from alkyl having 1 or 2 carbon atoms,halogen and nitro.
 2. A compound as in claim 1 in which n is
 1. 3. Acompound as in claim 1 in which n is
 2. 4. A compound as in clain 1 inwhich R₁ is hydrogen and R₂ is 2-methylphenyl or di- or tri-substitutedphenyl wherein the substituents are methyl or chlorine.
 5. A compound asin claim 1 in which R₁ is methyl and R₂ is selected from the groupconsisting of phenyl, phenyl substituted with 1 or 2 methyl groups,monohalophenyl and 2-naphthyl.
 6. A compound as in claim 1 selected fromthe group consisting of 2-(2,5-dimethylphenylmethylsulfonyl)-pyridineN-oxide, 2-(2,4,6-trimethylphenylmethylsulfonyl)-pyridine N-oxide,2-(2,6-dichlorophenylmethylsulfonyl)-pyridine N-oxide,2-(2,4-dichlorophenylmethylsulfinyl)-pyridine N-oxide,2-(2,6-dichlorophenylmethylsulfinyl)-pyridine N-oxide,2-(1-[4-methylphenyl]ethylsulfonyl)-pyridine N-oxide,2-(2,3,6-trichlorophenylmethylsulfonyl)-pyridine N-oxide,2-(2-methylphenylmethylsulfonyl)-pyridine N-oxide,2-(1-[4-fluorophenyl]ethylsulfonyl)-pyridine N-oxide,2-(1-[2,5-dimethylphenyl]ethylsulfonyl)-pyridine N-oxide,2-(2,3,6-trichlorophenylmethylsulfinyl)-pyridine N-oxide,2-(1-phenylethylsulfonyl)pyridine N-oxide,(1-[2-naphthyl]ethylsulfonyl)pyridine N-oxide,2-(1-[4-chlorophenyl]ethylsulfonyl)pyridine N-oxide,2-(1-[4-bromophenyl]ethylsulfonyl)pyridine N-oxide,2-(2,3,6-trimethylphenylmethylsulfonyl)pyridine N-oxide, and2-(2,3,6-trimethylphenylmethylsulfinyl)-pyridine N-oxide.
 7. A compoundas in claim 1 selected from the group consisting of2-(2,5-dimethylphenylmethylsulfonyl)pyridine N-oxide,2-(2,6-dichlorophenylmethtylsulfinyl)pyridine N-oxide,2-(1-[2,5-dimethylphenyl]-ethylsulfonyl)pyridine N-oxide,2-(2,4,6-trimethylphenylmethylsulfonyl)pyridine N-oxide,2-(1-[2-naphthyl]-ethylsulfonyl)pyridine N-oxide,2-(1-[4-chlorophenyl]-ethylsulfonyl)pyridine N-oxide,2-(1-[4-methylphenyl]-ethylsulfonyl)pyridine N-oxide, and2-(2,3,6-trimethyl-phenylmethylsulfinyl)pyridine N-oxide.
 8. A compoundas in claim 1 which is 2-(2,5-dimethylphenylmethylsulfonyl)pyridineN-oxide.
 9. A compound as in claim 1 which is2-(2,6-dichlorophenylmethylsulfinyl)pyridine N-oxide.
 10. A compound asin claim 1 which is 2-(1-[2,5-dimethylphenyl]ethylsulfonyl)pyridineN-oxide.
 11. A compound as in claim 1 which is2-(2,4,6-trimethylphenylmethylsulfonyl)pyridine N-oxide.
 12. A compoundas in claim 1 which is 2-(2-naphthyl-1-ethylsulfonyl)pyridine N-oxide.13. A compound as in claim 1 which is2-(1-[4-chlorophenyl]ethylsulfonyl]pyridine N-oxide.
 14. A compound asin claim 1 which is 2-(1-[4-methylphenyl]ethylsulfonyl)pyridine N-oxide.15. A compound as in claim 1 which is2-(2,3,6-trimethylphenylmethylsulfinyl)pyridine N-oxide.
 16. Aherbicidal composition comprising a chemical as in claim 1, in aherbicidally effective amount, in admixture with an inert carriertherefor.